toruble operating ic7000 with AH4 tuner

Discussion in 'General Technical Questions and Answers' started by AB1QX, May 3, 2012.

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  1. AB1QX

    AB1QX Subscriber QRZ Page

    I am a newly minted extra, back in the hobby after a nearly 50 year hiatus. My ic 7000 was initially operated
    into a MFJ window/balcony antenna (12ft whip w/ loading coil) and operated flawlessly. I purchased an AH4
    tuner and attempted operation into the prescribed 23 ft wire against a counterpoise. While the tuner does
    seem to provide a decent match (typically 1.2--1.3 vswr), all manner of strange operations are also seen.
    Specifically, the 7000 will change bands and modes during transmit, usually on the third or fourth keying.
    Occasionally, it will also invoke unprogrammed memory channels also. If keyed on 6 meters the radio seems to "reset": turns off then goes through the power-up sequence. I purchased this tuner after reading the glowing reviews seen in all quarters but personally am having no luck at all. What am I doing wrong?
  2. KJ3N

    KJ3N Ham Member QRZ Page

    Not a lot of detail here.

    1) Where is the AH-4 in relation to the 7000? For example, how far apart are the two?

    2) How close is the actual antenna to the 7000 and power supply?

    3) Are you using the remote head cable for the 7000, or is the head attached to the body?

    You've gone from what is a not so efficient antenna to something that is more effective at coupling 23 feet of wire (about twice what you had before) to the transmitter. You're probably seeing the results of an increase in radiated RF field strength. This is more than likely a simple case of RF getting back into the radio (and possibly the power supply), wreaking havoc with the circuitry.

    That's my best guess, given the information provided.
  3. AB1QX

    AB1QX Subscriber QRZ Page

    To elucidate (a little, anyway)--
    Everything is in close proximity and the front panel is on the radio. I would agree with your diagnosis, although
    the distances were the same if not closer with the MFJ antenna. I did add a heavier p/s (35A linear) at the same time(replacing a 15A switcher); maybe infiltration via the power cord is a candidate. Thanks, that hadn't occoured to me.
  4. KJ3N

    KJ3N Ham Member QRZ Page

    Not trying to be a PITA, but "close proximity" doesn't tell me much. Is everything in the same room? What actual distances are we talking about? Is the problem worse on some bands than others?

    Sorry, but the MFJ antenna is, IMO, a POS. So was the B&W AP-10 that the MFJ is modeled after. Not a very efficient antenna, particularly below 15m. You were probably not getting a lot of your power actually radiating from the antenna. More than likely, a good portion of it was wasted as heat, or sucked up by coil losses.

    You've gone from a 12 foot radiating element to a 23 foot one. With a decent counterpoise, you've probably increased your antenna efficiency from 10-15% with the MFJ (I assume it's the 1621 or the 1622) to 50-75% with the AH-4.

    If there is any way to get more separation between the AH-4 / antenna and the 7000 / power supply, I'd encourage you to do so.
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    Is Your System Grounded properly ?
  6. KJ3N

    KJ3N Ham Member QRZ Page

    Non-sequitur. Grounding has very little to do with this problem. This is proximity to a strong RF field. Toroids on every lead of the equipment would be a better solution.
  7. AC0VH

    AC0VH Ham Member QRZ Page

    You probably need to put a choke on the coax and control lines between the radio and tuner. I had this same problem when I first tried using a window line fed doublet with my AH-4. The tuner would find solutions, but since there is no balun in the tuner the radio-to-tuner cables were becoming part of the antenna. Common mode chokes on both fixed it for me.

    But one thing to note is that if you choke the coax and control cables, the tuner ground side is still RF hot. Touching metal on it while transmitting could burn you. A better way might be to build a balun to put between the tuner output and the quasi-balanced antenna.

    These guys are designed to feed a random wire over ground and be grounded themselves, so everything is unbalanced and ground referenced. When you stray from that you have to think about what voltages are developed and where current is going to flow.
    Last edited: May 3, 2012
  8. AB1QX

    AB1QX Subscriber QRZ Page

    Thanks so much for all the responses, they are much appreciated. My previous apparatus was the MFJ 1625 (whip, coil, LC tuner), the separation between the P/S, exciter, and tuner was very small, in all cases less than 15 ft. It appears my next move will be feedline chokes
    (line coils) followed by ferrites and toroids and possibly a balun. Further thoughts are of course welcome.
  9. KJ3N

    KJ3N Ham Member QRZ Page

    Which is nothing more than the 1622 with the addition of a tuner. The AH-4 setup is more efficient, thus the higher RF field, thus the problems.

    Which also explains some of the problem. I've seen people post about having a VHF/UHF rig and power supply do weird things, then come to find out the mag-mount antenna is sitting on the power supply, or only 10 feet away.

    Have you experimented with different power levels?
  10. AC0VH

    AC0VH Ham Member QRZ Page

    KJ3N's suggestion to make sure there is enough physical separation should be highly considered. If you're really only 15 feet from the antenna that could easily be it. Your old antenna was more or less a fancy dummy load, the field was likely less intense. It's easy to check and would still be a problem even if you do need chokes ultimately. Does it still do this at 10% of RF power?
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